Chromium plating using fume- and mist-depressant



United States Patent 3,480,662 'CHROMIUM PLATING USING FUME- AND MIST-DEPRESSANT Reuven Merker, 3601 Johnson Ave., Riverdale, N.Y. 10471, and Salvatore Lucca, 691 4th St., Secaucus, NJ. 07094 No Drawing. Filed Mar. 28, 1966, Ser. No. 537,700

Int. Cl. C23b 5/06 US. Cl. 20451 4 Claims ABSTRACT OF THE DISCLOSURE Mist and fume formation encountered during the electrolysis of aqueous acidic chromium solutions is abated by introducing into the solution a depressant compound having the empirical formula R-A (S 03M) x The present invention is related to improvements in the electrodeposition of chromium from aqueous chromeplating baths and, more particularly, it is related to highly stable additives for such baths which are capable of reducing to a very substantial degree the foundation of spray and mist during the electrolytic process.

The electrodeposition of chromium from aqueous acidic chromium solutions takes place, as it is well known, with the evolution of large quantities of hydrogen at the cathode and of oxygen and ozone at the insoluble anodes. The undesirable spray and mist of chromic acid result from the violent bursting of gas bubbles of high surface energy which are released by the electrolytic process. The mist and spray which result from this hubble bursting is a cause of great concern, due to the corrosiveness and high toxicity to the workers of these acidic evolutions. The well known deleterious contaminating effect on other plating baths, such as nickel, copper, cadmium and zinc, is conventionally abated in large scale, commercial operations by the employment of powerful ventilation systems to continuously remove the contaminant as it is formed.

For example, to remove the mist formed in a 2000 gallon tank installation requires an exhaust of as much as 10,000 cubic feet per minute of contaminated air to enable safe continuous production. The use of powerful ventilation is expensive both as capital investment and as to cost of upkeep and maintenance. Furthermore, in wintertime, such ventilation is responsible for an abnormal aud cost abstraction of the heated air in the electrolysis room. Also to be considered, is that not all of the spray and mist are removed from the area adjacent to the plating tank, regardless of the ventilation system employed. This is especially true in the case of wide plating tanks. A certain amount of chromic acid mist always contaminates the air, especially when stray air currents pass over the tank during electrodeposition.

From the standpoint of toxicity, the maximum safe concentration of chromium trioxide is now considered to be approximately one tenth of one milligram per cubic meter of inhaled air. In addition to the disadvantages connected with adequate ventilation, one must consider the loss of chromic acid in the exhausted air, which may amount to about 30% of the acid used in the electrodeposition, and the corrosion effected on the metallic parts of the ventilating system.

The problems arising as a result of chromic acid evolutions from ele'ctrolytic tanks were recognized almost from the very inception of chrome plating and attempts have been made from time to time to prevent, or at least, minimize the formation of these sprays and mists. As examples of attempted solutions, it has been suggested to form a protective blanket on the surface of the bath by the use of various oils, floating objects of plastic material, wetting agents of non-ionic character, and others. None of these attempts has been found satisfactory. For example, foaming agents such as ethoxylated alkyl aryls have been found to be short lived, because the blanket of foam over the bath is very acidic and the chromic acid is a strong oxidizer, so that the blanketing compounds are rapidly broken down. It has also been suggested to blanket the bath with tailed fluorocarbon compounds, which, besides providing a low blanket, create a low surface density. However, their utilization is limited to small tanks, because of the considerable expense connected with their use. Furthermore, these tailed fluorocarbon compounds cannot be employed in hard chromium plating, that is, in electrodeposition of heavy chrome coatings, because they cause pitting in the coating.

It is, therefore, a first object of the present invention to provide for a fume and mist depressant which affords a good, dense and thick foam which is stable under electrolytic conditions and also under highly acid and oxidizing conditions.

It is another object of the present invention to provide for a fume and mist depressant which, while economically inexpensive, does not cause pitting under any circumstances.

It is a further object of the invention to provide for a fume and mist depressant which does not have catalytic efiects in the bath and which affords a protective blanket over the bath which continues well after electrolysis has subsided.

It is a still further object of this invention to provide for a fume and mist depressant which aids in the rinsing operations of the plated parts.

The depressant for fumes and mist of chromic acid, in accordance with the invention may be represented empirically by the formula Br-A (SOaM) x wherein R is a straight-chained or a branch-chained radical having from 1 to 30 carbon atoms therein; A is an aryl, imidazol, or a cyclic compound; M is a metal; and x is an integer ranging from 1 to 4 inclusive.

The following are typical compositions within the breadth of the above empirical formula and are shown in order to illustrate the chemical structure of certain specifically suitable depressants.

where R is a C -C straight-chaincd or branch-chained radical; M is a metal; and x is 1, 2, 3 or 4.

where R is a C straight-chained or branch-chained radical; R" is hydrogen or a straight-chained radical having from 1 to 8 carbon atoms; M is sodium, potassium, calcium or magnesium; and z is 1 or 2.

(c) sodium heptadecylbenzimidazol monosulfonate (d) disodium heptadecylbenzimidazol disulfonate (e) sodium heptadecylmethylbenzimidazol monosulfonate (f) disodium heptadecylmethylbenzimidazol disulfonate (g) The sodium salt of n-methylheptadecylbenzimidazoline sulfonic acid.

All these compounds, and in fact the compounds encompassed by the a-bove-cited general empirical formula, may be employed either alone or in conjunction with other and known compounds, such as ethoxyl-ated dodecyl phenols or disodium 4-dodecylated oxydibenzene sulfonate, in order to give to these known depressants a synergistic and beneficial eifect.

The following examples illustrate the advantages and operability of the depressants of the invention.

EXAMPLE I A 600-gal10n solution was prepared, according to standard industrial procedures, for chrome plating purposes. The solution contained 55 ounces of chromic acid per gallon of solution and a catalyst in a ratio of 100:1 as it is well known in the art. The plating operation was conducted at a temperature of approximately 120 F. and at a current density of 100 amperes/ square foot.

An initial charge of about one-half to one fluid ounce per 100 gallons of solution was introduced into the bath, the charge consisting of the compound (c) given hereabove, namely sodium heptadecylbenzimidazol monosulfonate. A dense blanket resulted over the bath, 2 inches thick, which completely suppressed all acid fumes evolutions and all misting from the plating bath. The surface tension was reduced to about 32 dynes/cm. A total amount of one pint of compound (c) was employed to maintain the above-stated conditions in the bath for 10 hours of continuous plating operations. It was, successive- 1y, found that the final rinsing of the plated part was considerably aided by the addition of the depressant compound EXAMPLE II Another plating operation was performed under conditions identical to those given in the previous Example I.

An initial charge of about of one fluid ounce per 100 gallons of solution was introduced into the bath, the charge consisting of the compound ((1) given hereabove, namely, disodium heptadecylbenzimidazol disulfonate. Again, a dense blanket resulted over the bath, about 2 inches thick, which completely suppressed all chromic acid fumes and misting. The surface tension was reduced to about 33 dynes/ cm. A total amount of one pint of compound (d) was employed to maintain the abovestated conditions in the bath for 11 hours of continuous plating operations. Again, the final rinsing of the plated part was found to be considerably aided by the addition of compound (d).

EXAMPLE III The conditions of Example I were repeated. This time, about 1 fluid ounce per gallons of solution was initially charged, which consisted of compound (a) in which R was a C straight-chained radical, M was sodium, and x was 2. Again, a dense blanket resulted over the bath, more than 2 inches thick, which completely suppressed all evolutions of fumes and mist. The surface tension was reduced to about 32 dynes/cm. A total amount of V5 of one pint of the compound was employed during the entire 10 hour plating operation to maintain the above-mentioned suppressing eifects on the bath. Rinsing of the plated part was, once again, aided noticeably by the compound.

What is claimed is:

1. In a process of electroplating chromium from a chromium plating solution which contains a fumeand mist-depressant therein, the improvement wherein there is present assaid depressant a sufiicient amount to substantially abate the evolution of acidic fumes and mist a compound of the formula SO33 x wherein R is a straight-chain or a branchedchain radical having 1 to 30 carbon atoms therein; M is a metal, and x is an integer ranging from 1 to 4 inclusive, said compound being the sole mistand fume-depressant in said solution.

2. The process of claim 1 wherein M is sodium.

3. The process of claim 2 wherein R is a C straightchain radical and x is 2.

4. The process of claim 3 wherein the compound is added to the solution in amounts ranging from one-half to one fluid ounce per one hundred gallons of solution, as an initial charge.

References Cited UNITED STATES PATENTS 1,755,179 4/ 1930 Giinther 260--505 2,463,497 3/ 1949 Smith et a1 260505 2,750,334 6/ 1956 Brown 204-51 3,041,257 6/1962 Cope et al. 204-51 3,084,111 4/1963 Strauss et a1. 20451 3,341,434 9/1967 Passal 20451 3,342,709 9/ 1967 Johnson 20451 JOHN H. MACK, Primary Examiner G. L. KAPLAN, Assistant Examiner 

